The figure rose from 22.6 percent in the first quarter, according to Boston-based app analytics firm Localytics

More than a third of all Android smartphones in the U.S. are equipped with 4G and the number is rapidly increasing, according to a study by app analytics firm Localytics.

Localytics' data shows that in the third quarter of 2011, 36.6 percent of Android phones were equipped with 4G, growing from 22.6 percent in the first quarter of this year. The Boston firm included smartphones enabled with HSPA+ (High-Speed Packet Access+), LTE (Long-Term Evolution), and WiMax in its study.

"What's more, this number is increasing rapidly -- since the beginning of the year, the percentage of Android devices that are 4G-capable has grown by more than 50 percent, culminating at a full third of the Android ecosystem," Daniel Ruby, director of online marketing at Localytics, said in a blog post. Android handset makers have been "extremely aggressive" in their adoption of high-speed mobile data protocols, he said.

Android 4G growth is driven by Sprint's HTC Evo 4G and Samsung's Epic 4G phones along with Verizon's HTC Thunderbolt and Samsung's Droid Charge, Localytics noted. With the Thunderbolt, Evo 4G, and Droid Charge ranked as numbers one, two and three in the most popular 4G Android phone charts.

The myTouch 4G, T-Mobile's most popular 4G Android, is ranked fifth in the overall charts. AT&T's most popular 4G Android smartphone is the Motorola Atrix.

Android competitors iPhone and BlackBerry do not yet offer 4G phones. It remains to be seen whether rumors will prove true that the iPhone 5 will support 4G. A July study by electronics review site Retrovo found that 61 percent of iPhone owners don't care if the new iPhone has 4G and will buy or consider buying one regardless of 4G. The same study noted that a third of iPhone owners think they already own a 4G phone.